Plasma enhanced hollow fiber gas separation membrane chemical vapor deposition method and application

Abstract

The invention discloses a plasma enhanced hollow fiber gas separation membrane chemical vapor deposition method and application. The hollow fiber gas separation membrane material is a polymer which is specifically selected from any one of polysulfone (PSf), polyether sulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI) and polyamideimide. A hollow fiber membrane is prepared by adopting a dry spraying / wet spinning process, a surface skin layer of the hollow fiber membrane is functionally modified by utilizing a plasma enhanced chemical vapor deposition technology, and an excitation gas source is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3. The technology can regulate and control the chemical properties of the cortex micropore structure and the pore channel of the hollow fiber membrane, a compact, ultrathin, uniform and controllable atomic-scale selection layer is formed, and the gas separation performance is remarkably improved. Meanwhile, the plasma treatment flow is simple, the cost is low, the reaction is controllable, and the method is suitable for industrial large-scale treatment. The obtained plasma enhanced chemical vapor deposition hollow fiber membrane also has excellent mechanical properties and anti-plasticizing stability, and has a wide prospect in actual gas separation application.

Description

Technical Field

[0001] The invention relates to the technical field of gas separation membranes, and in particular to a method and application of plasma enhanced hollow fiber gas separation membrane chemical vapor deposition. Background Art

[0002] Gas separation membrane technology is a pressure-driven, phase-change-free gas separation process. Due to its advantages such as high energy efficiency, low cost, simple maintenance, small footprint, and green and pollution-free, it has become an ideal choice to replace traditional separation methods (such as pressure swing adsorption and cryogenic distillation). It has shown good application prospects in pre-combustion CO2 capture, post-combustion CO2 capture, hydrogen separation and recovery, air separation, natural gas helium extraction, and natural gas decarbonization.

[0003] In the past few decades, microporous polymers have been used to prepare various membrane forms, including hollow fiber, plate-and-frame, and spiral, due to their low cost and ease of processing. Among them, asymmetric hollow fiber membranes (HFMs) are widely used in industrial gas separation due to their unique structural properties - the combination of a dense skin layer and a porous sublayer, as well as high surface area to volume ratio, self-supporting, flexibility, and easy large-scale production.

[0004] The main challenge of gas separation membranes is that the gas separation performance of membrane materials faces trade-off limitations, and it is difficult to break through the upper limit of gas separation permeability and selectivity. Existing commercial hollow fiber membrane materials, such as 5218, P84, CA, PESf, etc., have low selectivity due to the wide pore size distribution of the polymer, and the separation performance needs to be improved urgently.

[0005] Plasma enhanced chemical vapor deposition (PECVD) is a post-processing method that excites a specific gas source into highly reactive free electrons, ions and other substances under the action of an electric field, so that it reacts in situ and at the atomic level with the sample surface. It has the advantages of in-situ reaction, controllable reaction, low cost, and large-scale processing. It is expected to achieve the modification of polymer microporous structure and break through the upper limit of gas separation. Chinese patent CN 118320629 A provides a plasma modification method for a self-polymerized microporous polymer gas separation membrane. By regulating the microporous structure of the membrane material, an efficient gas selective transmission channel is constructed, thereby significantly improving the oxygen / nitrogen diffusion selectivity of the gas separation membrane. However, due to the high cost of synthesizing self-polymerized microporous polymer materials and the difficulty in the enlarged preparation of polymers, it is impossible to achieve the enlargement and application of large-area gas separation membranes. Chinese patent CN106102885 A discloses a method for treating the surface of a polymer membrane using plasma. By plasma treating a partial area of ​​the polymer membrane surface, active substances are introduced to improve the gas separation performance of the membrane material. However, this method is difficult to achieve uniform treatment over a large area, and therefore it is difficult to effectively regulate the entire membrane pore structure. The bombardment of the membrane surface may also affect the service life of the membrane. In addition, although the above two patents point out that the polymer membrane can be selected from a hollow fiber membrane, there is no description of the specific preparation method of the hollow fiber membrane.

[0006] The present application needs to provide a method for plasma-enhanced chemical vapor deposition of hollow fiber gas separation membranes and a preparation process of the hollow fiber gas separation membranes. Through plasma treatment, the surface cortex of the hollow fiber membrane is functionally modified, and its cortex microporous structure and pore chemical properties are regulated to form a dense, ultra-thin, uniform and controllable atomic-level selective layer to improve gas separation performance. Summary of the invention

[0007] The purpose of the present invention is to propose a method and application of plasma enhanced chemical vapor deposition of hollow fiber gas separation membranes, to obtain hollow fiber membranes with high gas separation performance, excellent mechanical properties and anti-plasticization stability, and to apply them to industrial gas separation scenarios.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the gas separation membrane material of the present invention is a polymer, specifically selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamide-imide.

[0010] Preferably, the gas separation membrane is an asymmetric hollow fiber membrane prepared by dry-jet / wet-spinning process.

[0011] In a second aspect, the present invention provides a method for preparing a hollow fiber gas separation membrane, comprising the following steps:

[0012] (1) Adding a certain weight ratio of polymer, solvents A and B, and non-solvents C and D into a reaction kettle equipped with a mechanical stirrer, stirring the mixture for 1-7 days, and after the mixture is completely dissolved, degassing for 12-48 hours to obtain a spinning solution;

[0013] (2) preparing a core liquid by mixing solvent A and non-solvent C in a certain weight ratio;

[0014] (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare primary fibers, which are then pulled onto a winding wheel for further solidification;

[0015] (4) Remove the spun fiber from the winding wheel and soak it in water for 1-5 days, changing the water every 12 hours. After that, soak the fiber in solvent E and solvent F alternately for solvent exchange, changing the solvent every 0.5-3 hours, and soaking for a total of 3-24 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 120-180°C for 12-48 hours to remove any residual solvent to obtain the final fiber;

[0016] (5) Prepare a 2-10wt% polydimethylsiloxane (PDMS) solution in solvent G to post-treat the fiber. After heating the solution at 80-120°C for 2-12 hours, immerse the fiber in the solution for 1-30 minutes, and then drain the excess solution. Hang and dry the fiber in a fume hood for 8-24 hours, and then cure the fiber in a vacuum drying oven at 80-120°C for 2-12 hours. The final hollow fiber gas separation membrane is obtained.

[0017] The temperature of the reactor in step (1) is 25-55°C;

[0018] Preferably, the weight ratio of step (1) is: polymer 10-40wt%, solvent A 30-90wt%, solvent B 0-35wt%, non-solvent C 0-25wt%, non-solvent D 0-5wt%;

[0019] Preferably, the sum of the weight ratios in step (1) is 100%;

[0020] Preferably, the polymer in step (1) is selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamide-imide;

[0021] Preferably, the solvent A in step (1) is selected from one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO); the solvent B is selected from one or more of tetrahydrofuran (THF), dichloromethane (CH2Cl2) and chloroform (CHCl3); the non-solvent C is selected from one or more of methanol, ethanol and water; the non-solvent D is selected from one or more of lithium chloride (LiCl), lithium nitrate (LiNO3), lithium perchlorate (LiClO4) and lithium sulfate (Li2SO4).

[0022] The weight ratio of step (2) is 0-95wt% of solvent A and 5-100wt% of non-solvent C;

[0023] Preferably, the sum of the weight ratios in step (2) is 100%.

[0024] Step (3) The spinneret aperture is 0.2-0.7 mm, the temperature is 25-75°C, and the spinning solution extrusion speed is 3-18 mL / min -1 ; Core liquid flow rate is 1-6mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 2.5-30 cm. The coagulation bath uses deionized water at a temperature of 25-55°C. The spinning wheel speed is 5-30 min. -1 ;

[0025] Preferably, in step (3), the ratio of the spinning solution extrusion speed to the core liquid flow rate is 3:1.

[0026] In step (4), the solvent E is selected from one or both of methanol and ethanol; and the solvent F is selected from one or both of n-hexane and n-heptane.

[0027] The solvent G in step (5) is selected from one or more of n-hexane, n-heptane and n-pentane.

[0028] In a third aspect, the present invention provides a method for plasma enhanced chemical vapor deposition of a hollow fiber gas separation membrane, comprising the following steps:

[0029] (1) placing the hollow fiber gas separation membrane in a reaction chamber of a plasma enhanced chemical vapor deposition (PECVD) device, and evacuating the reaction chamber for 30 minutes to reach a certain vacuum degree;

[0030] (2) introducing a specific gas source into the reaction chamber to maintain the reaction chamber at a certain pressure;

[0031] (3) The gas source is excited into plasma through an electric field, and reacts with the hollow fiber membrane at a certain power and temperature for a certain time to obtain a plasma-assisted surface functionalized hollow fiber gas separation membrane.

[0032] The plasma enhanced chemical vapor deposition (PECVD) device in step (1) uses a radio frequency (RF) generator, and the reaction chamber is a quartz tube with a size of Φ150*1500mm;

[0033] Preferably, the hollow fiber gas separation membrane in step (1) is placed 0-20 cm below the RF coil outside the reaction chamber;

[0034] Preferably, the vacuum degree after the vacuum treatment in step (1) reaches 0.1-1Pa.

[0035] The gas source in step (2) is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3;

[0036] Preferably, the gas source in step (2) is ultra-high purity (UHP) grade gas;

[0037] Preferably, the pressure of the reaction chamber in step (2) is maintained at 5-200 Pa.

[0038] In step (3), the power of the gas source excitation is 10-300W, the reaction temperature is 0-100°C, and the reaction time is 0.5-30 minutes.

[0039] In a fourth aspect, the present invention provides a use of a plasma enhanced chemical vapor deposition of a hollow fiber gas separation membrane, wherein the plasma enhanced chemical vapor deposition hollow fiber membrane is used for any one of pre-combustion CO2 capture, post-combustion CO2 capture, hydrogen separation and recovery, air separation, natural gas helium extraction and natural gas decarbonization.

[0040] Compared with the prior art, this application has the following beneficial effects:

[0041] The polymer material described in the present application is selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamide-imide, which is easy to obtain and convenient to process. The present application adopts a dry spray / wet spinning process to prepare a hollow fiber membrane, and uses plasma enhanced chemical vapor deposition technology to functionally modify its surface cortex, and the excitation gas source is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3. This technology can regulate the microporous structure and pore chemical properties of the hollow fiber membrane cortex to form a dense, ultra-thin, uniform and controllable atomic-level selection layer, which significantly improves the gas separation performance. At the same time, the plasma treatment process is simple, the cost is low, the reaction is controllable, and it is suitable for large-scale industrial processing. The plasma enhanced chemical vapor deposition hollow fiber membrane obtained in the present application also has excellent mechanical properties and anti-plasticization stability, and has broad prospects in practical gas separation applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of a plasma enhanced chemical vapor deposition (PECVD) device of the present invention.

[0043] Figure 2 It is a transmission electron microscope (TEM) morphology image of the cross section of the hollow fiber membrane before and after CF4 plasma treatment in Example 1 of the present invention.

[0044] Figure 3 This is a diagram of the mechanical modulus of the hollow fiber membrane surface before and after CF4 plasma treatment in Example 1 of the present invention.

[0045] Figure 4 This is a pore size distribution diagram of the hollow fiber membrane before and after O2 plasma treatment in Example 4 of the present invention.

[0046] Figure 5 It is the He / CH4 separation performance of the hollow fiber membrane under different gas source treatments in Examples 1-7 of the present invention.

[0047] Figure 6 It is the O2 / N2 separation performance of the hollow fiber membrane under different gas source treatments in Examples 1-7 of the present invention. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0049] Example 1

[0050] This embodiment provides CF4 plasma enhanced chemical vapor deposition 5218 Preparation method of hollow fiber gas separation membrane:

[0051] (1) In a 25°C reactor equipped with a mechanical stirrer, add 500 g of 5218 polymer, 1130 g of solvent N-methylpyrrolidone (NMP) and 285 g of non-solvent ethanol (EtOH), the weight ratio is 5218 polymer 26.2wt%, NMP 58.9wt%, EtOH 14.9wt%, the mixture was stirred for 4 days, and after it was completely dissolved, it was degassed for 24 hours to obtain a spinning solution;

[0052] (2) preparing a core liquid by mixing 950 g of solvent N-methylpyrrolidone (NMP) and 50 g of non-solvent water in a weight ratio of 95 / 5 wt %;

[0053] (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare the nascent fiber, which is then pulled onto a winding wheel for further solidification. The spinneret aperture is 0.4 mm, the temperature is 25 °C, and the spinning solution extrusion speed is 6 mL min -1 ; core liquid flow rate is 2mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 10 cm. The coagulation bath uses deionized water at a temperature of 25°C. The spinning wheel speed is 20 min. -1 ;

[0054] (4) Remove the spun fiber from the winding wheel and soak it in water for 3 days, changing the water every 12 hours. After that, soak the fiber in methanol and n-hexane alternately for solvent exchange, changing the solvent every 0.5 hour, for a total of 3 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 180°C for 12 hours to remove any residual solvent to obtain the final fiber;

[0055] (5) Prepare a 2 wt% polydimethylsiloxane (PDMS) solution in n-heptane to post-treat the fiber. After heating the solution at 100°C for 6 hours, immerse the fiber in the solution for 30 minutes, and then drain the excess solution. Hang and dry the fiber in a fume hood for 24 hours, and then cure the fiber in a vacuum drying oven at 80°C for 2 hours. The final hollow fiber gas separation membrane is obtained;

[0056] (6) placing the hollow fiber gas separation membrane in a reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, directly below the RF coil, and evacuating the reaction chamber to a vacuum degree of 0.1 Pa;

[0057] (7) introducing ultra-high purity (UHP) grade CF4 into the reaction chamber to maintain the pressure of the reaction chamber at 65 Pa;

[0058] (8) CF4 was excited into plasma by an electric field with an excitation power of 50 W and reacted with the membrane surface at 25 °C for 3 min to obtain a plasma-enhanced chemical vapor deposition hollow fiber gas separation membrane, named Matri-CF4-50W-65Pa-3min.

[0059] Example 2

[0060] This embodiment provides CF4 plasma enhanced chemical vapor deposition 5218 Preparation method of hollow fiber gas separation membrane, CF4 plasma treatment The preparation method of 5218 hollow fiber gas separation membrane refers to Example 1, except that the plasma treatment temperature is changed from 25°C to 50°C, and the treatment time is changed from 3 minutes to 10 minutes. The obtained plasma enhanced chemical vapor deposition hollow fiber gas separation membrane is named Matri-CF4-50W-65Pa-10min.

[0061] Example 3

[0062] This embodiment provides a method for preparing an O2 plasma enhanced chemical vapor deposition polyethersulfone (PES) hollow fiber gas separation membrane:

[0063] (1) In a 25° C. reaction kettle equipped with a mechanical stirrer, 500 g of polyethersulfone (PES) polymer, 1078 g of solvent N-methylpyrrolidone (NMP) and 128 g of non-solvent water (H2O) were added, with a weight ratio of 29.4 wt% of polyethersulfone (PES) polymer, 63.1 wt% of NMP and 7.5 wt% of H2O. The mixture was stirred for 4 days, and after being completely dissolved, it was degassed for 24 hours to obtain a spinning solution;

[0064] (2) preparing a core liquid by mixing 500 g of non-solvent ethanol and 500 g of water in a weight ratio of 50 / 50 wt %;

[0065] (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare the nascent fiber, which is then pulled onto a winding wheel for further solidification. The spinneret aperture is 0.7 mm, the temperature is 25 °C, and the spinning solution extrusion speed is 3 mL min -1 ; The core liquid flow rate is 1 mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 10 cm. The coagulation bath uses deionized water at a temperature of 25°C. The spinning wheel speed is 5 min. -1 ;

[0066] (4) Remove the spun fiber from the winding wheel and soak it in water for 3 days, changing the water every 12 hours. After that, soak the fiber in methanol and n-hexane alternately for solvent exchange, changing the solvent every 0.5 hour, for a total of 3 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 180°C for 12 hours to remove any residual solvent to obtain the final fiber;

[0067] (5) Prepare a 2 wt% polydimethylsiloxane (PDMS) solution in n-heptane to post-treat the fiber. After heating the solution at 80°C for 2 hours, immerse the fiber in the solution for 1 minute, and then drain the excess solution. Hang and dry the fiber in a fume hood for 8 hours, and then cure the fiber in a vacuum drying oven at 80°C for 2 hours. The final hollow fiber gas separation membrane is obtained;

[0068] (6) placing the hollow fiber gas separation membrane in a reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, directly below the RF coil, and evacuating the reaction chamber to a vacuum degree of 0.1 Pa;

[0069] (7) introducing ultra-high purity (UHP) grade O2 into the reaction chamber to maintain the pressure in the reaction chamber at 13 Pa;

[0070] (8) O2 was excited into plasma by an electric field with an excitation power of 50 W and reacted with the membrane surface at 25 °C for 2 min to obtain a plasma-enhanced chemical vapor deposition hollow fiber gas separation membrane, named PES-O2-50W-13Pa-2min.

[0071] Example 4

[0072] This embodiment provides a method for preparing an O2 plasma enhanced chemical vapor deposition polyethersulfone (PES) hollow fiber gas separation membrane. The method for preparing an O2 plasma treated polyethersulfone (PES) hollow fiber gas separation membrane refers to Example 3, except that the reaction chamber pressure is maintained at 5 Pa. The obtained plasma enhanced chemical vapor deposition hollow fiber gas separation membrane is named PES-O2-50W-5Pa-2min.

[0073] Example 5

[0074] This embodiment provides a method for preparing a H2 plasma enhanced chemical vapor deposition cellulose acetate (CA) hollow fiber gas separation membrane:

[0075] (1) In a 50°C reactor equipped with a mechanical stirrer, 500 g of cellulose acetate (CA) polymer, 1355 g of solvent (N-methylpyrrolidone (NMP) and 218 g of tetrahydrofuran (THF)) and 109 g of non-solvent ethanol (EtOH) were added, with a weight ratio of 23 wt% of cellulose acetate (CTA) polymer, 62 wt% of NMP, 10 wt% of THF and 5 wt% of EtOH. The mixture was stirred for 1 day, and after being completely dissolved, it was degassed for 24 hours to obtain a spinning solution;

[0076] (2) 1000 g of non-solvent water as the core liquid;

[0077] (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare the nascent fiber, which is then pulled onto a winding wheel for further solidification. The spinneret aperture is 0.4 mm, the temperature is 25 °C, and the spinning solution extrusion speed is 3 mL min -1 ; The core liquid flow rate is 1 mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 20 cm. The coagulation bath uses deionized water at a temperature of 30 °C. The spinning wheel speed is 20 min. -1 ;

[0078] (4) Remove the spun fiber from the winding wheel and soak it in water for 3 days, changing the water every 12 hours. After that, soak the fiber in methanol and n-hexane alternately for solvent exchange, changing the solvent every 0.5 hour, for a total of 3 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 180°C for 12 hours to remove any residual solvent to obtain the final fiber;

[0079] (5) Prepare a 5 wt% polydimethylsiloxane (PDMS) solution in n-hexane to post-treat the fiber. After heating the solution at 80°C for 2 hours, immerse the fiber in the solution for 1 minute, and then drain the excess solution. Hang and dry the fiber in a fume hood for 24 hours, and then cure the fiber in a vacuum drying oven at 80°C for 2 hours. The final hollow fiber gas separation membrane is obtained;

[0080] (6) placing the hollow fiber gas separation membrane in a reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device at a position 10 cm below the RF coil, and evacuating the reaction chamber to a vacuum degree of 0.1 Pa;

[0081] (7) introducing ultra-high purity (UHP) grade H2 into the reaction chamber to maintain the pressure in the reaction chamber at 3 Pa;

[0082] (8) H2 was excited into plasma by an electric field with an excitation power of 150 W and reacted with the membrane surface at 25 °C for 3 min to obtain a plasma-enhanced chemical vapor deposition hollow fiber gas separation membrane, which was named CTA-H2-150W-3Pa-3min.

[0083] Example 6

[0084] This embodiment provides a method for preparing a CH4 plasma enhanced chemical vapor deposition polyetherimide (PEI) hollow fiber gas separation membrane:

[0085] (1) In a 25° C. reactor equipped with a mechanical stirrer, 500 g of polyetherimide (PEI) polymer, 578 g of solvent (N-methylpyrrolidone (NMP) and 576 g of tetrahydrofuran (THF)) and 16.8 g of non-solvent lithium nitrate (LiNO3) were added, with a weight ratio of 30 wt% of polyetherimide (PEI) polymer, 34.5 wt% of NMP, 34.5 wt% of THF, and 1 wt% of LiNO3. The mixture was stirred for 2 days, and after being completely dissolved, it was degassed for 24 hours to obtain a spinning solution;

[0086] (2) preparing a core liquid by mixing 950 g of solvent N-methylpyrrolidone (NMP) and 50 g of non-solvent water in a weight ratio of 95 / 5 wt %;

[0087] (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare the nascent fiber, which is then pulled onto a winding wheel for further solidification. The spinneret aperture is 0.2 mm, the temperature is 25 °C, and the spinning solution extrusion speed is 4.5 mL min -1 ; core liquid flow rate is 1.5mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 10 cm. The coagulation bath uses deionized water at a temperature of 25°C. The spinning wheel speed is 22 m / min. -1 ;

[0088] (4) Remove the spun fiber from the winding wheel and soak it in water for 3 days, changing the water every 12 hours. After that, soak the fiber in methanol and n-hexane alternately for solvent exchange, changing the solvent every 1 hour, for a total of 6 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 180°C for 12 hours to remove any residual solvent to obtain the final fiber;

[0089] (5) Prepare a 2 wt% polydimethylsiloxane (PDMS) solution in n-hexane to post-treat the fiber. After heating the solution at 80°C for 2 hours, immerse the fiber in the solution for 1 minute, and then drain the excess solution. Hang and dry the fiber in a fume hood for 12 hours, and then cure the fiber in a vacuum drying oven at 80°C for 2 hours. The final hollow fiber gas separation membrane is obtained;

[0090] (6) placing the hollow fiber gas separation membrane in a reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device at a position 20 cm directly below the RF coil, and evacuating the reaction chamber to a vacuum degree of 0.1 Pa;

[0091] (7) introducing ultra-high purity (UHP) CH4 into the reaction chamber to maintain the pressure in the reaction chamber at 10 Pa;

[0092] (8) CH4 was excited into plasma by an electric field with an excitation power of 250 W and reacted with the membrane surface at 45 °C for 3 min to obtain a plasma-enhanced chemical vapor deposition hollow fiber gas separation membrane named PEI-CH4-250W-10Pa-3min.

[0093] Example 7

[0094] This embodiment provides a method for preparing a NH3 plasma enhanced chemical vapor deposition polysulfone (PSf) hollow fiber gas separation membrane:

[0095] (1) In a 25° C. reactor equipped with a mechanical stirrer, 500 g of polysulfone (PSf) polymer, 1104 g of solvent N-methylpyrrolidone (NMP) and 68.5 g of non-solvent water (H2O) were added, with a weight ratio of 30 wt% of polysulfone (PSf) polymer, 65.9 wt% of NMP and 4.1 wt% of H2O. The mixture was stirred for 2 days, and after being completely dissolved, it was degassed for 24 hours to obtain a spinning solution;

[0096] (2) preparing a core liquid by mixing 600 g of solvent N-methylpyrrolidone (NMP) and 400 g of non-solvent water in a weight ratio of 60 / 40 wt %;

[0097] (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare the nascent fiber, which is then pulled onto a winding wheel for further solidification. The spinneret aperture is 0.7 mm, the temperature is 25 °C, and the spinning solution extrusion speed is 9 mL min -1 ; core liquid flow rate is 3mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 5 cm. The coagulation bath uses deionized water at a temperature of 25 °C. The spinning wheel speed is 5 m / min. -1 ;

[0098] (4) Remove the spun fiber from the winding wheel and soak it in water for 5 days, changing the water every 12 hours. After that, soak the fiber in methanol and n-hexane alternately for solvent exchange, changing the solvent every 1 hour, for a total of 6 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 180°C for 12 hours to remove any residual solvent to obtain the final fiber;

[0099] (5) Prepare a 3 wt% polydimethylsiloxane (PDMS) solution in n-pentane to post-treat the fiber. After heating the solution at 80°C for 2 hours, immerse the fiber in the solution for 5 minutes, and then drain the excess solution. Hang and dry the fiber in a fume hood for 12 hours, and then cure the fiber in a vacuum drying oven at 80°C for 2 hours. The final hollow fiber gas separation membrane is obtained;

[0100] (6) placing the hollow fiber gas separation membrane in a reaction chamber of a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) device, directly below the RF coil, and evacuating the reaction chamber to a vacuum degree of 0.1 Pa;

[0101] (7) introducing ultra-high purity (UHP) NH3 into the reaction chamber to maintain the pressure in the reaction chamber at 78 Pa;

[0102] (8) NH3 was excited into plasma by an electric field with an excitation power of 50 W and reacted with the membrane surface at 25 °C for 5 min to obtain a plasma-enhanced chemical vapor deposition hollow fiber gas separation membrane, named PSf-NH3-50W-78Pa-5min.

[0103] Application Example 1

[0104] In this application example, a transmission electron microscope (TEM) is used to characterize the cross-sectional morphology of the hollow fiber membrane before and after CF4 plasma treatment in Example 1.

[0105] The results are as follows Figure 2 As shown, compared with before treatment, the plasma treated hollow fiber gas separation membrane surface forms a dense, ultra-thin, uniform fluorinated selective layer of 5 nm. This proves that the method provided by the present invention can achieve uniform treatment of the membrane surface, which will be beneficial to improve gas separation selectivity.

[0106] Application Example 2

[0107] In this application example, an atomic force microscope (AFM) is used to characterize the nano-scale mechanical properties of the surface of the hollow fiber membrane before and after the CF4 plasma treatment in Example 1.

[0108] The results are as follows Figure 3As shown, compared with the surface mechanical modulus of the hollow fiber gas separation membrane treated with plasma (2.70 MPa), the surface mechanical modulus increased to 15.47 MPa, which proves that the method provided by the present invention can make the membrane have excellent mechanical properties.

[0109] Application Example 3

[0110] This application example uses CO2 physical adsorption to study the pore size distribution of the hollow fiber membrane before and after O2 plasma treatment in Example 3.

[0111] The results are as follows Figure 4 As shown in the figure, after O2 plasma treatment, the micropores and ultramicropores of the hollow fiber membrane are distributed toward the smaller pore size region, which proves that the method provided by the present invention can modify the pore structure of the membrane material.

[0112] Application Example 4

[0113] This application example tests the pure gas permeabilities of He, H2, CO2, O2, N2 and CH4 of the plasma enhanced chemical vapor deposition hollow fiber gas separation membranes prepared in Examples 1-7 at 35°C and 2 bar, and calculates the permeabilities of H2 / N2, H2 / CH4, He / N2, He / CH4 ( Figure 5 ), CO2 / CH4 and O2 / N2( Figure 6 ), the test results are shown in Table 1.

[0114] Table 1 Gas permeability and selectivity of plasma enhanced chemical vapor deposition hollow fiber gas separation membrane

[0115]

[0116] As shown in Table 1, Figure 5 and Figure 6 As shown, different plasma enhanced chemical vapor deposition hollow fiber gas separation membranes all show excellent gas separation performance. As the CF4 plasma treatment time increases, the permeability increases and the selectivity decreases due to the occurrence of etching. As the O2 gas source pressure in the reaction chamber decreases, the degree of treatment increases, the permeability decreases, and the selectivity increases. In short, the method provided by the present invention can enable the gas separation performance of the membrane material to break through the upper limit of gas separation, and has good application prospects in a variety of separation scenarios.

Claims

1. A method and application of plasma enhanced hollow fiber gas separation membrane chemical vapor deposition, characterized in that: The gas separation membrane material is a polymer, specifically any one selected from polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamideimide.

2. A gas separation membrane according to claim 1, characterized in that: The gas separation membrane is an asymmetric hollow fiber membrane prepared by dry-jet / wet-spinning process.

3. The method for preparing a hollow fiber gas separation membrane according to claims 1 and 2, characterized in that: The preparation method comprises the following steps: (1) Adding a certain weight ratio of polymer, solvents A and B, and non-solvents C and D into a reaction kettle equipped with a mechanical stirrer, stirring the mixture for 1-7 days, and after the mixture is completely dissolved, degassing for 12-48 hours to obtain a spinning solution; (2) preparing a core liquid by mixing solvent A and non-solvent C in a certain weight ratio; (3) The spinning solution and the core solution are co-extruded into a coagulation bath through a spinneret for phase separation to prepare primary fibers, which are then pulled onto a winding wheel for further solidification; (4) Remove the spun fiber from the winding wheel and soak it in water for 1-5 days, changing the water every 12 hours. After that, soak the fiber in solvent E and solvent F alternately for solvent exchange, changing the solvent every 0.5-3 hours, and soaking for a total of 3-24 hours. Hang and dry the fiber in a fume hood for 30 minutes, and then dry the fiber in a vacuum drying oven at 120-180°C for 12-48 hours to remove any residual solvent to obtain the final fiber; (5) Prepare a 2-10wt% polydimethylsiloxane (PDMS) solution in solvent G to post-treat the fiber. After heating the solution at 80-120°C for 2-12 hours, immerse the fiber in the solution for 1-30 minutes, and then drain the excess solution. Hang and dry the fiber in a fume hood for 8-24 hours, and then cure the fiber in a vacuum drying oven at 80-120°C for 2-12 hours. The final hollow fiber gas separation membrane is obtained.

4. The preparation method according to claim 3, characterized in that: The temperature of the reactor in step (1) is 25-55°C; Preferably, the weight ratio of step (1) is: polymer 10-40wt%, solvent A 30-90wt%, solvent B 0-35wt%, non-solvent C 0-25wt%, non-solvent D 0-5wt%; Preferably, the sum of the weight ratios in step (1) is 100%; Preferably, the polymer in step (1) is selected from any one of polysulfone (PSf), polyethersulfone (PES), polyimide (PI), polybenzimidazole (PBI), cellulose acetate (CA), polyetherimide (PEI), and polyamide-imide; Preferably, the solvent A in step (1) is selected from one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO); the solvent B is selected from one or more of tetrahydrofuran (THF), dichloromethane (CH2Cl2) and chloroform (CHCl3); the non-solvent C is selected from one or more of methanol, ethanol and water; the non-solvent D is selected from one or more of lithium chloride (LiCl), lithium nitrate (LiNO3), lithium perchlorate (LiClO4) and lithium sulfate (Li2SO4).

5. The preparation method according to claim 3 or 4, characterized in that: The weight ratio of step (2) is 0-95wt% of solvent A and 5-100wt% of non-solvent C; Preferably, the sum of the weight ratios in step (2) is 100%.

6. The preparation method according to any one of claims 3 to 5, characterized in that: Step (3) The spinneret aperture is 0.2-0.7 mm, the temperature is 25-75°C, and the spinning solution extrusion speed is 3-18 mL min -1 ; Core liquid flow rate is 1-6mL min -1 The distance between the spinneret and the coagulation bath, i.e. the air gap, is 2.5-30 cm. The coagulation bath uses deionized water at a temperature of 25-55°C. The spinning wheel speed is 5-30 min. -1 ; Preferably, in step (3), the ratio of the spinning solution extrusion speed to the core liquid flow rate is 3:

1.

7. The preparation method according to any one of claims 3 to 6, characterized in that: In step (4), the solvent E is selected from one or both of methanol and ethanol; and the solvent F is selected from one or both of n-hexane and n-heptane.

8. The preparation method according to any one of claims 3 to 7, characterized in that: The solvent G in step (5) is selected from one or more of n-hexane, n-heptane and n-pentane.

9. The method for plasma enhanced hollow fiber gas separation membrane chemical vapor deposition according to claim 1, characterized in that: The method comprises the following steps: (1) placing a hollow fiber gas separation membrane in a reaction chamber of a plasma enhanced chemical vapor deposition (PECVD) device, and evacuating the reaction chamber for 30 minutes to reach a certain vacuum degree; (2) Introducing a specific gas source into the reaction chamber to maintain the reaction chamber at a certain pressure; (3) The gas source is excited into plasma through an electric field, and reacts with the hollow fiber membrane at a certain power and temperature for a certain time to obtain a plasma-assisted surface functionalized hollow fiber gas separation membrane.

10. The preparation method according to claim 9, characterized in that: The plasma enhanced chemical vapor deposition (PECVD) device in step (1) uses a radio frequency (RF) generator, and the reaction chamber is a quartz tube with a size of Φ150*1500mm; Preferably, the hollow fiber gas separation membrane in step (1) is placed 0-20 cm below the RF coil outside the reaction chamber; Preferably, the vacuum degree after the vacuum treatment in step (1) reaches 0.1-1Pa.

11. The method according to claim 9 or 10, characterized in that: The gas source in step (2) is selected from one or more of H2, CH4, Ar, N2, CF4, O2 and NH3; Preferably, the gas source in step (2) is ultra-high purity (UHP) grade gas; Preferably, the pressure of the reaction chamber in step (2) is maintained at 5-200 Pa.

12. The method according to any one of claims 9 to 11, characterized in that: In step (3), the power of the gas source excitation is 10-300W, the reaction temperature is 0-100°C, and the reaction time is 0.5-30 minutes.

13. The use of plasma enhanced hollow fiber gas separation membrane chemical vapor deposition according to claim 1, characterized in that: The plasma treated hollow fiber gas separation membrane is used for any one of pre-combustion CO2 capture, post-combustion CO2 capture, hydrogen separation and recovery, air separation, natural gas helium extraction and natural gas decarbonization.

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